The interaction of Chlorophyll derivative photosensitizer CPD3 with mouse lung cancer DNA

CPD₃ is a new kind of photosensitizer (PS) with promising applications in photodynamic therapy (PDT) for anticancer treatment. The binding properties of CPD₃ to mouse lung cancer cell DNA have been investigated by using absorption spectroscopy. In neutral CPD₃-DNA mix solution in NS, the peak wavelengths of absorption bands of CPD₃ (B and Q band) do not change basically but the intensities of them do decrease with increase of the concentration of the DNA, in addition, some new red-shifted absorption bands appear in the spectra and become stronger with increasing the concentration of the DNA and with prolonging incubation period of the sample solution. In basic mix solution (pH=8.0), the situation above is not observed and absorption bands of CPD₃ are not yet changed in the peak position and intensity even though the concentration of DNA in the solution is high enough to 1.75times10^-5mg/l. The study shows that some free CPD₃ molecules bind to DNA to form a "complex" through intensive groove and hydrogen bonding interaction between them in a proper time period. However, the electrostatic interaction between CPD₃ and the DNA is not important for formation of the "complex". The intercalative binding model included groove, hydrogen bonding, and spatial obstacle interaction would be preferable. The photobleaching (PB) properties of the CPD₃ solution with and without the DNA are investigated under irradiating with LD at 674 nm and 20 mW. For the former, PB lifetime of CPD₃ is 49.3 seconds, for the latter, 96.2 seconds. Both the decay curves obey single exponential drop rule exactly. The results show that the PB of CPD₃ is a single excited state reaction; the intercalative binding between CPD₃ and DNA can increase the rate constant for PB reaction. The electrophoresis graph of the bleached solution indicates that the DNA is destroyed basically.- - The study indicates the CPD₃ is an efficient and stable PS for PDT.